jj2000.j2k.codestream.writer

Class BitOutputBuffer

java.lang.Object

jj2000.j2k.codestream.writer.BitOutputBuffer

public class BitOutputBuffer
extends Object

This class implements a buffer for writing bits, with the required bit stuffing policy for the packet headers. The bits are stored in a byte array in the order in which they are written. The byte array is automatically reallocated and enlarged whenever necessary. A BitOutputBuffer object may be reused by calling its 'reset()' method.

NOTE: The methods implemented in this class are intended to be used only in writing packet heads, since a special bit stuffing procedure is used, as required for the packet heads.

Field Summary

Fields

Modifier and Type	Field and Description
(package private) int	avbits The number of available bits in the current byte
(package private) byte[]	buf The buffer where we store the data
(package private) int	curbyte The position of the current byte to write
static int	SZ_INCR The increment size for the buffer, 16 bytes.
static int	SZ_INIT The initial size for the buffer, 32 bytes.

Constructor Summary

Constructors

Constructor and Description
BitOutputBuffer() Creates a new BitOutputBuffer width a buffer of length 'SZ_INIT'.

Method Summary

Methods

Modifier and Type	Method and Description
byte[]	getBuffer() Returns the byte buffer.
int	getLength() Returns the current length of the buffer, in bytes.
void	reset() Resets the buffer.
byte[]	toByteArray(byte[] data) Returns the byte buffer data in a new array.
String	toString() Prints information about this object for debugging purposes
void	writeBit(int bit) Writes a bit to the buffer at the current position.
void	writeBits(int bits, int n) Writes the n least significant bits of 'bits' to the buffer at the current position.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

buf

byte[] buf

The buffer where we store the data

curbyte

int curbyte

The position of the current byte to write

avbits

int avbits

The number of available bits in the current byte

SZ_INCR

public static final int SZ_INCR

The increment size for the buffer, 16 bytes. This is the number of bytes that are added to the buffer each time it is needed to enlarge it.

See Also:

Constant Field Values

SZ_INIT

public static final int SZ_INIT

The initial size for the buffer, 32 bytes.

See Also:

Constant Field Values

Constructor Detail

BitOutputBuffer

public BitOutputBuffer()

Creates a new BitOutputBuffer width a buffer of length 'SZ_INIT'.

Method Detail

reset

public void reset()

Resets the buffer. This rewinds the current position to the start of the buffer and sets all tha data to 0. Note that no new buffer is allocated, so this will affect any data that was returned by the 'getBuffer()' method.

writeBit

public final void writeBit(int bit)

Writes a bit to the buffer at the current position. The value 'bit' must be either 0 or 1, otherwise it corrupts the bits that have been already written. The buffer is enlarged, by 'SZ_INCR' bytes, if necessary.

This method is declared final to increase performance.

Parameters:

bit - The bit to write, 0 or 1.

writeBits

public final void writeBits(int bits,
             int n)

Writes the n least significant bits of 'bits' to the buffer at the current position. The least significant bit is written last. The 32-n most significant bits of 'bits' must be 0, otherwise corruption of the buffer will result. The buffer is enlarged, by 'SZ_INCR' bytes, if necessary.

This method is declared final to increase performance.

Parameters:

bits - The bits to write.

n - The number of LSBs in 'bits' to write.

getLength

public final int getLength()

Returns the current length of the buffer, in bytes.

This method is declared final to increase performance.

Returns:

The currebt length of the buffer in bytes.

getBuffer

public final byte[] getBuffer()

Returns the byte buffer. This is the internal byte buffer so it should not be modified. Only the first N elements have valid data, where N is the value returned by 'getLength()'

This method is declared final to increase performance.

Returns:

The internal byte buffer.

toByteArray

public byte[] toByteArray(byte[] data)

Returns the byte buffer data in a new array. This is a copy of the internal byte buffer. If 'data' is non-null it is used to return the data. This array should be large enough to contain all the data, otherwise a IndexOutOfBoundsException is thrown by the Java system. The number of elements returned is what 'getLength()' returns.

Parameters:

data - If non-null this array is used to return the data, which mus be large enough. Otherwise a new one is created and returned.

Returns:

The byte buffer data.

toString

public String toString()

Prints information about this object for debugging purposes

Overrides:

toString in class Object

Returns:

Information about the object.